Soewardi was born in a Javanese aristocracy, his family ranked to the royal house of Yogyakarta. Thanks to his family's priyayi (Javanese nobility) background, he was able to access the colonial public education, a luxury that was unattainable by most of common population in the Indies. He graduated from basic education in ELS (Dutch Primary School). Then he continued his study to STOVIA, a medical school for native students. However, he failed to graduate because suffered an illness. Later he worked as a journalist and wrote for numbers of newspapers, among others are, Sediotomo, Midden Java, De Expres, Oetoesan Indies, Kaoem Moeda, Tjahaja Timoer and Poesara. During his career in printed media, he was considered a talented and accomplished writer. His style of writing is popular, communicative and yet imbued with freedom idealism and anti-colonialism sentiments.

Besides tenacious as a young reporter, Soewardi was also active in social and political organizations. Since the establishment of Boedi Oetomo in 1908, he was active in their propaganda service to socialize and promote public awareness of Indonesia as a national unity (especially in Java), at the time emphasize about the importance of the unity of the nation. He also organized Boedi Oetomo first congress in Yogyakarta.

Young Soewardi was also a member of the Insulinde, a multi-ethnic organization that dominated by Indo activist. This organization was advocating for self-rule in the Dutch East Indies. One of the prominent figure in this organization was Ernest Douwes Dekker. Later, Soewardi was invited to join the party, when Douwes Dekker established Indische Partij.

In 1913, the Dutch East Indies government sought to collect money to fund the centennial anniversary of Dutch independence from France back in 1813. The donations was draw from Dutch East Indies citizens, which also includes bumiputera (indigenous people). This decision has ignited critical oppositions and negative reactions from pro-independence nationalists, including Soewardi. He wrote several critical columns, such as "Een maar ook voor Allen Allen voor Een" or "One for All, All for One". However, the most famous piece of Ki Hadjar Dewantara's column is "If I'm A Dutch" (original title: "Als ik een Nederlander was"), printed in De Expres newspaper on 13 July 1913. The content of his article fiercely criticized the colonial government of Netherlands Indies. The citation of his writing, as followsː

If I am a Dutchman, I would not celebrate an independence ceremony in the country where we ourselves, denied their rights of freedom. Consistent with the way of the mind, it was not only unfair, but also inappropriate to ask the Inlander (native Indonesian) to provide funds for such festivities. The very idea of the independence festivities alone is quite insulting for them, and now we also scour their pockets. Come on, away with the physical and spiritual humiliation! Had I am a Dutchman, a particular case that offends our friends and countrymen, is the fact that the inlanders required to participate and bankrolled an activity that do not have the slightest importance for them.[citation needed]

Some Dutch officials doubted that this piece was actually written by Soewardi, because compared to his earlier writings, there are some differences in style and vocabulary.[citation needed] Even if it is true, that it was Soewardi's writing, they suspected that there might be some active roles of Douwes Dekker that influenced Soewardi to write in such tone.[clarification needed]

Soewardi's writings that criticize the colonial government was considered by the colonial authority as a subversive, sensitive and divisive material that feared might incite a popular revolt and upset the delicate social order of the Dutch East Indies. As the consequences, Soewardi was captured under the order of Governor General Idenburg, and sentenced to exile in Bangka Island.[clarification needed] However, both his colleagues, Douwes Dekker and Tjipto Mangoenkoesoemo, protested on his behalf, and eventually in 1913, the three of them were exiled to the Netherlands instead. This three pro-independence activist figures, Soewardi, Douwes Dekker and Tjipto, later known as the Tiga Serangkai or the "triad". Soewardi at that time was only 24 years old.

During his exile in the Netherlands, Soewardi was active in the Indonesia students organization, the Indische Vereeniging (Indies Association).

This is where he contemplated the idea on advancing science education for natives, by obtaining the Europeesche certificate, a prestigious education diploma which later became the foundation on establishing educational institutions he would founded. In this study, Soewardi was fascinated by the ideas of Western education figures, such as Froebel and Montessori, as well as Indian education movement activist; Santiniketan and Tagore family. These underlying influences would contributed to Soewardi's idea on developing his own educational system.

On September 1919, Soewardi returned home to Java, Dutch East Indies. Immediately, he joined his brother on establishing a school in his native hometown. His educational background and his teaching experiences then proved to be useful on developing the concept for teaching in school, as he founded the Nationaal Onderwijs Instituut Ampel or the national college. During the time of colonial social discrimination in the early 20th century, education was only made possible for the elites; the colonial Dutch people and a handful of Javanese noblemen families. Education at that time was not made available for native commoners. In July 1922, Soewardi established Taman Siswa school in Yogyakarta, a Javanese educational movement that strive to provide education for native population.

When he reached 40 years of age, according to the Javanese beliefs based upon Javanese calendar, he is required to changed his name to ward of misfortunes that might befell upon him. Thus he choose "Ki Hadjar Dewantara" as his new name. He also scrapped the Javanese gentility title Raden Mas in front of his name. It was a gesture to demonstrate his support for social equality, to disregard the rigid social stature of Javanese society. Ki Hadjar intended to be freely interacted with people of all social backgrounds, and close to them in both physical and soul.

Ki Hadjar Dewantara has coined a famous proverb on describing his ideals for education. Rendered in Javanese, the maxim reads: Ing ngarso sung tulodo, ing madyo mangun karso, tut wuri handayani. Which translates: "(for those) in front should set an example, (for those) in the middle should raise the spirit, and (for those) behind should give encouragement". The proverb is used as the principle of Taman Siswa. Today, part of this maxim, Tut Wuri Handayani is used as the motto of Indonesian Ministry of Education. It was meant to describe an ideal teacher, after transmitting knowledge to their students, the teacher would stand behind their students and give them encouragements in their quest for knowledge.

During the days of Japanese occupation, Ki Hajar's activities in the field of politics and education still continues. When the Japanese government established the People Power Center (Pusat Tenaga Rakyat or Putera) in 1943, Ki Hajar was appointed as one of its leaders, in addition to Sukarno, Muhammad Hatta and K.H. Mas Mansur.

In the first cabinet of the Republic of Indonesia in the 1950s, Ki Hajar Dewantara was appointed as Indonesian Minister of Education and Culture. In 1957 he received an honorary doctorate honoris causa from Indonesia's oldest university, Gadjah Mada University.

He died in Yogyakarta on 26 April 1959 and was buried in Taman Wijaya Brata cemetery.

In recognition for his dedications and accomplishments on pioneering public education in Indonesia, he was declared as the Father of Indonesian National Education, a national hero, and his birthday is appointed as the National Education Day, through Presidential Decree no. 305 of 1959, dated 28 November 1959.

Taman Siswa has established Dewantara Kirti Griya Museum in Yogyakarta. The museum was built to commemorate, preserve and promote the thought, values and ideals of Ki Hajar Dewantara, the founder of Taman Siswa. In this museum, there are objects and works of Ki Hajar Dewantara. Museum collections includes his works, papers, concepts, important documents and correspondence of Ki Hajar during his lifetime as a journalist, educator, humanist and as an artist. These documents has been recorded on microfilms and some are laminated with the help the National Archives of Indonesia.

Ki Hajar Dewantara advocates that education should be made possible and available for all people, regardless of their sex, race, ethnicity, culture, religion, economic and social status, etc. He argued that education should be based on the values of common humanity, human freedom and the rights to seek knowledge.

Ki Hajar Dewantara's birthday is now celebrated as Indonesian National Education Day. He is also credited for coined the motto; Tut Wuri Handayani, today used by the ministry of education. An Indonesian navy training ship, KRI Ki Hajar Dewantara, bears his name in honor. His portrait immortalizes him in the 20,000 rupiah bank note denomination in 1998.